Nutation system



11, 1955 J. s. HOHL ETAL 2,699,502

NUTATION SYSTEM Filed Jan. 9, 1953 Invewhors: John 25., Hohl E|Hz5 Their ttowne g Unitecl States Patent O 1 z,e99soz NIJIATION SYSTEM John S. Hohl and.Ellis T. Davis,- Schenectady, N. Y. a

signors to General Electric Company, a -corporation of New York Application January 9, 1953, Serial N0. 330,492 11 Clainns'. '(Cl. 250 3355) This invention relates to an irnproved :nutation system and more particularly to such a system which is adapted for imparting nutation rnovements ofhigh speed to high frequenoy electromagnetic radiation antennas of a directional variety such as are usedfor radar systems, in :a scanning operation.

in nutation systems of the type described above; a1- though the radiation antenna which is to be driven is generally a dish-shaped member of light weight conductive material, at the nutation frequencies which -are desired, which may fall, for instanee, within -the range of from eighteen -to twerlty-four cycles per second, or higher, the accelerations of the various portions of the antenna and nutation system are quite high. Considerable difi"multy has thus been encouhtered in obtaining a sn'1ooth operating system which does not have excessiv e mechanical vibration, excessive bearing wear, and which does not require excessively high power -input and an extremely -heavy mounting framework.

Accordingly, lt is one important object of the presen't invention 110 provide an improved nutation system having reduced vibration, requiring less power, andinvolving less wear n moving parts and permitting a lighter supporting frarnework.

The term nutationin this patent application is defined as.a repeated oscillatory motio11 *of a pivotally mounted body about its pivot. This oscillation 0r nutation nlove- 1nent may describea rectilinear path, a.circular path er any other non-rectilinear path. 111 some apparatus requiring directional antenna elements ior.high frequency electromagnetic radiation, such as radar apparatus, it is very ciesirable from the standpoint of =th'e desig'n of the remainder of the system to obtain rectilinear untation. The most convenient and practical driving mo- -tors, however, provide for rotational .rnovement. Un- :fortunately, the mechanisms Whieh mlist be employed to impart a rectilinear nutation motion of the -antnna derived .from a .circular motion of a drivemotor generally increase the vibration and wear difficulties and the allied problems outlined above.

Aecordingly, it is a further objecf of the present invention to provide an improved vibration free:nutation syslem for obtaining recitilinear nutation from a mfa- -tional driving motor.

:In carrying out the objects of this invention, a untation systern may be employed in which the drive motor is arranged and connected to drive the remainder of the system at a point corresponding to the eentef of percussion for every phase and dit'ection of operatior1 of the drive motor.

For a rnore thorough understanding of the i'nvei1ti'ori, reference should be made to the following Specification and the accor'npanying drawings, in which:

Fig. 1 is a perspective drawing of a first preferred en1bodiment of this invention.

Fig. 2 is a similar perspective drawing of a secbnd preferred embodiment cf this invention for p'roviding rectilinear nutation.

Re'ferring more particularly to Fig. 1;there is sh oWn a radiation dish 10 which is pivotally mounted by means of integral brac'kets lland 1 2 t0 a yoke mtzmber 13 which may be in the forin of an e'li11tical hoop for relative rotation about a vertical axis 9. The yoke 13 is in turn mounted by means of pivots 14 and 15 to fixed mountings 16 and 17 for pivtal movement of the yoke 13 and the dish 10 aboutthe horiz'ontal aXis 8 determined by the pins 14 and 15. The point of intersection of axes 8 and 9 may be referred to belov'v as the pivot point.

An operating rod 18, which is fastened as an integral part of dish 10, may extend outwardly therefr0m for connection -to a crank 19 which may be im the form horizontal aXis 8 Will only be the iriertia -iaiished. The-counterweights are mountecl 2,699502 Patented Jan. 11, 1955 -tively referred to beloW as a dr1ve mechanism.

1rwi11 be Seen that for vertical cornponents of movernenr of crank 19 and the operating rod 18 the dish 10 and the yoke 13 Will both be rotated about the determin'ed by pivots 14 and 15. "lhe ineriia of the systeni for vertical nutation Will therefore be the surn of the ir1ertias -of the dish 10 and the yol e 131 .l*or horizontal con1ponents ot rnovement of operating rod 16, however, only the dis'n 10 will move about the vertiea'l axis 9 as determined by the pivots at bracket-s 11 and 12 and the inertia opposing rotation of the dish 10. uoumerweights 24arxd 25 a're threrore provided at ho'rizontahy spaced c'e'ntral p0sitions on dish 10, preferably near the horizonral a-xis of pins 14 and 15 to increase the inerria o'r dish 10 about the vertical axis With0llt appreciable iiacreae irl.inerti about the horizontal axis. lne inertia of diSh 10 about the V6II1Cll ax1s is thus caused to eX- actlj/ ei=fesponcl io the -combined inertia of the dish 10 a1'1dthe yol e 13 about the horizontal axis. lt Will be obViou's that with propr spacing and proper mass of the -eounterweight's 24 and z:;, this may be acco1nby means of arrhs which extnd back towards the crank 19 so that the cerlter of gravity of the entire system is displaced point in thedirection ofcrank 19.

'l-he le'ngtl'r or the opetating rod l8 is chosen so that the point ot' attachinenttot crank 19 to the operating rod 18 correpondsito the Center of percussion o1 the ciouble -piVted fiutation System including the dish 10 and the yoke 13 about the axes 8 and 9. The center of pereussion' -iS defi1ed as the point at which the percussive aetio1l f a llow' o1'1 a pivoted body is the sarne as if the Whole Irlass of the body were c0ncentrated at the point. B'y driV'ingthe nutation systern at its center of pe'r'eu'ss'ibri,- the r etore, the re'action forces at the bearings 1'6 arid 17 a11d 11 and 12 =becorne substantially nil even thl'lgh the devic is driven at frequencies -as high as twenty four cyc'les per second or more, for instance, in whichthe rapid acc'elerations are practically analagous to the pef'cussive action of a blow. With the addition of the counterweights 24 and 25, equalizing the inertia of the Systerri about the vertical and horizontal axes, the centers of Percussion of the nutation system for the horizontal aiis 8 and for the vertical axis 9 exactly edinoide at thep0irit Where the operating rod 18 is driven by the crank 19. Theref0re there is substantially no cha1le" in the lad on the motor 22 during the various crank 19. The transiden "rlcin'1 vertical m horizontal motion is therefore s'rnoot'h; ciu'iet and vibrationlrss regardless of the speed o'r' frequency with which the system is driven.

*simpl6 firethod for calculating and determining the exagit Center df fijercssiofi of a System such as that shoWn in Fig'. I sind the exact length for operating rod 18 is as f0l'l*owsl- The Center of percussion is identical to the center df osc'illatiri, and the -center of oscillation is defined as a pomr on a line drawn frorn the center of g'raivity of a Pivoteci body, Per-pendicular to the pivot aXis, whos e motion is the sarhe as it would be were the efitir m'zis df the body" there concentrated and allow'ed w vibrate' as zi= pefidulunr. The distance from the center of osoillat'ion" to the pivot axis, which may be called the radi'us f oscillation, is therfore the same as the horizontal pivot ..The apparatus is WhereT is the period of vibration about the axis of suspension in seconds, g is the acceleration due to gravity in reet per second per second, which is a constant known value tor a given locality, and 1r is the geometr ic comstant representing the ratio between the circumterence and the diameter of a circle. By employing the above formula, the center of oscillation and the center of percussion, and the length I' the operating rod 18 rnay be determined by pivotally mounting the nutation systern including the yol e 13 and the dish 10, swinging the mechan1sm about either axis under the force 01 gravity and tin1ing the resulting oscillations. When the oscillation time is known, it may be substituted in the above formula for the 'l and the required length L of operating rod 18 may thereiore be directly determined by computing the rormula value. Also, if the oscillations about horizontal axis 8 do not correspond exactly in time With the oscillations about vertical axis 9, the counterweights 24 and 25 n1ay be appropriately altered in mass or position to obtain an exact iaentity of these tirnes of oscillation so that the centers of percussion for oscillation about these two axes will correspond exactly at a point w'nere the crank 19 may be attached to operating rod 18.

in ernbodirndnt of Fig. l, the operating rod 18 is shown as aligned perpendicular to both axes 8 and 9 and the nutau'on movernent provided by this structure for dish 10 describes a circular pattern. If a rectilinear nutation movernent is desired, the end of operating rod 18 can be moved vertically up and down by rneans of a suitable reciprocating motor rather than the rotational motor 22 which is shown. ln such an arrangement the pivots at 11 and 12 could be eliminated as well as the entire yoke 13 and the counterweights 24 and 25. The pins 14 and 15 could be attached directly 10 the dish 10 and the center of percussion about the horizontal axis 8 would be the only center of percussion which need be considered. Unlortunately, available reciprocating motors are not as satisfactory an d reliable Ior this purpose as are rotating motors, and lt is convenient, thererore, to employ an alternative ernbodiment of the nutation system of Fig. 1 such as is shown in Fig. 2 in order to obtain rectilinear nutation from rotary motor power.

In the ernbodirnent of Fig. 2, only a rectilinear component of the movernent of crank 19 is actually utilized and the horizontal pivot mountings 14 and 15 are connected to the dish 10, rather than to the yoke 13 and conversely the operating rod 18 and the counterweights 24 and 25 are connected to the yoke 13 by porting arms, rather to a U-shape in order to conveniently accomplish this. In this ernbodirnent, since the dish 10 has no rotat1on whatsoever about the vert1cal axis 9, the counterweights 24 and 25 must be selected for the proper mass and position to provide the yoke member 13 plus the counterweights with as great an inertia about the verhcal ax1s 9 as the cornbined inertia of all of these components plus the dish 10 about the horizontal axis 8.

another objective in the selection 01 the masses and positions of counterwe1ghts 24 and 25 is that the center of percussion should coincide With the po1nt of attachrnent ployment of the pendulurn principle and formula de-' scribed at sorne length above in connection with Fig. 1. swung about axis 8, and the time of oscillation is recordecl and the pendulurn length or the distance frorn axis 8 to the center of percussion for that axis is then calculated. Sirnilarly, the system is swung about axis 9 and a sirnilar tirne observation is made and the center of percussion is then calculated for the system from axis 9. Suitable adjustrnent of the s1ze and positions of counterweights 24 and 25 may then be made in order to bring these together to determine the point at which operat1ng rod 18 and crank 19 should be attached.

The systern of Fig. 2 as well as the syst ern 01 Fig. 1 provides a very srnooth operating charactertstrc s1nce the load on motor22; Connected through crank 19, is again 1 substantially the sarne during all angles of each rotasuitable supthan to the dish 10. The yoke member 13 is changed from the shape of an oval hoop Of course,

tion. The load represented by the nutation system counected through operating rod 18 to cranl 19 is again exactly coumerbalancen by crank counterweight 20. The smoorhness ot operation which is obtainame with this embodiment is considered to be more spectacular s1nce the output motion ot' radiation dish member 10 represents a rectilinear pattern, while the input rrom motor 22 is a circular rotation. This embouiment is therefore particularly valuable for the many systems where a rectilinear oscillatory antenna nutation is most desired.

All of the bearings in each of the embodiments are prer'erably oi' the anti-friction type, such as those ernployrng rollers, balls, or "needle bearings, in order to obta1n maximum operating ease and a m1nirnum ower consumpuon, and the bearmg at the connect1on between operating rod 18 and C13.I1K 19 preferably includes a unrversal 0int or a self-aligning anti-friction bearing. ln eachof the emoodiments, the motor shaft 23 is preferahly ahgned on an axis which intersects the point at wnrch horizontal axis 8 and vertical axis 9 meet. If properly aligned, an ordinary anti-triction bearing may then be employed at the connection between operating rod 18 and crank 19.

lt yvill be obvious that it is possible to tilt the dish 10 w1th respect to either or both ot' the axes 8 and 9 Wh1le ma1ntaining the centers of gravity and percussion at the saure point by proper adjustment of the mass and pos 1t1ons ot counterweights 24 and 25. Such a tilted des1gn n1ay be very des1rable where other associated apparat us (not shown) must be placed near the dish 10 in posrt1ons which would otherwise interfere with the operaung rod 18, the motor 22 and associated components.

In the above description oii this invention it has been spec1fie l that the centers of percussion of the system about the hor1zontal and vertical axes 8 and 9 should exactly cor ncrde, that the system should be driven exactly at the corncrde nt centers of percussion, that the axes 8 and 9 should 1ntersect at a pivot point and therefore should l1e in the same plane, and that the pivot axes 8 and 9 should be perpendicular to one another and perpendicular to the operat1ng rod 18. lt is true that when all of these condrtrons exist precisely the maxirnum and best performance ls obtainable. lt will be realized, however, that some 01 the benefits of this inventioh may be obtained even though slight deviations are made from these ideal design condrtrons. It should be clearly understood that the greater such deviations may be, the greater the roughness of operation will De and the less the advantages of this mv ent1on will be apparent. The design limits beyond which no appreciable advantage of the invention will appear are as follows: (l) where the centers of percussion for rotation about the respective axes 8 and 9 do not coinerde, the distance from the pivot point to the further removegi center of percussion should not exceed cf the d1st ance frorn the pivot point to the nearer center of percussion; (2) the drive point to which the crank 19 is connected to operating rod 18 should not be displaced from the rnean center of percussion (a point rnidway between the non-coincident centers of percussion) by more than 20% of the distance frorn the pivot point to the mean oenter of percussion; (3) the pivot axes 8 and 9 need not 1ntersect and therefore necd not lie in the same plane. N0 1irnits are stated for the amount of permissible displacement between these axes since the other design limitatron s which are specified here will determine a practical 'l1rrnt on this displacement; (4) the angle between any pa1r of the three axes 8 and 9 and the axis of the operating rod 18 should not be decreased below 60 degrees.

The following claims are intended to define the valid scope of this invention over the prior.art and to cover all cha'nges' and modifications falling within the true spirit and valid scope of the invention.

What we clairn as new and desire to secure by Letters Patent of the United States is: 1

1. A nutation apparatus cornprising a member to be nutat ed, a yoke member pivotally connected thereto for relat 1ve rotation abo'ut a first axis, one of said members includ1ng piVotal supports for rotation about a second axis non-para'llel to said first axis, the other of said members mcluding at least orte counterbalancing weight for bringing the center of percussion for rotation thereof about said first aXis into coincidence with the center of percussion for rotation 'of the combination of said members about said second axis, said-other member also inchiding' an operating member extending to said coincident centers of percussion.

2. A nutation apparatus comprising a member to be nutate a yoke member pivotally connected thereto for relative rotation about a first axis, said yoke member including pivotal supports for rotation about a second axis nun-parallel to said first axis, said nutated member in cluding at least one counterbalancing Weight for bringing the center of percussion for rotation thereof about said first axis into coincidence with the center of percussion for rotation of the combination of said members about said second axis, said nutated member also including an operating member extending to said coincident centers of percussion.

3. A nutation apparatus comprising a member to be nutated, a yoke member pivotally connected thereto for relative rotation about a first axis, said nutated member including pivotal supports for rotation about a second axis non-parallel to said first axis, said yoke member including at least one counterbalancing weight for bringing the center of percussion for rotation thereof about said first axis into coincidence with the center of percussion for rotation of the combination of said members about said sec ond axis, said yoke member also including an operating rnember extending to said coincident centers of percuss1on.

4. A nutation apparatus comprising a member to be nutated, a yoke member pivotally connected thereto for relative rotation about a first axis, one of said members including pivotal supporting devices for support thereof for rotation about a second axis perpendicular to said first axis, the other of said members inclucling at least two balancing weights for making the center of percussion for rotation thereof about said first axis coincident with the center of percussion for rotation of the combination of said members about said second axis, said other member also including an operating rod extending therefrom away from both of said axes at least as far as to said center of percussion, and a drive mechanism connected to said operating rod at said center of percussion.

5. A nutation apparatus comprising a member to be nutated, a yoke member pivotally connected thereto for relative rotation about a first axis, said yoke member including pivotal supporting devices for support thereof for rotation about a second axis perpendicular to said first axis, said nutated member including at least two balancing weights for making the center of percussion for rotation thereof about said first axis coincident With the center of percussion for rotation of the combination of said members about said second axis, said nutated member also including an operating rod extending therefrom away frorn both of said axes at least as far as to said center of percussion, and a drive mechanism connected to said operating rod at said center of percussion.

6. A nutation apparatus cornprising a member to be nutated, a yoke member pivotally connected thereto for relative rotation about a first axis, said nutated member including pivotal supporting devices for support thereof for rotation about a second axis perpendicular to said first axis, said yoke member including at least two balancing weights for making the center of percussion for rotation thereof about said first axis coincident With the center of percussion for rotation of the combination of said members about said second axis, said yoke member also including an operating rod extending therefrom away from both of said axes at least as far as to said center ot' percussion, and a drive mechanism connected to said operating rod at said center of percussion.

7. A nutation apparatus cornprising a member to be nutated, a yoke member pivotally connected thereto for relative rotation about a first axis, one of said members including pivotal supporting devices for support thereof for rotation about a second axis substantially perpendicular to said first axis, the other of said members including at least two balancing weights for equalizing the moments of inertia and for making the eenters of percussion of the cornbination of said members coincident for movement about either axis, said other member also including an operating rod extending theretrom away from both of said axes at least as far as to said coincident centers of percussion, a drive mechanism comprising a motor having an output shaft, a crank mounted on said output shaft and connected to said operating rod at said center of percussion, said crank including a counterweight positioned diametrically opposite to the connection ot said operating rod for counterbalancing the load connected thereby.

8. A nutation apparatus cornprising a member to be nutated, a yoke member pivotally connected thereto for relative rotation about a first axis, said yoke member including pivotal supporting devices for support thereof or rotation about a second axis substantially perpendicular to said first axis, said nutated member including at least two balancing weights for equalizing the Inornents of inertia and for making the centers of percussion of the combination of said members coincident for rnovement about either axis, said nutated member also including an operating, rod extending therefrom away from both ot said axes at least as far as to said coincident centers of percussion, a drive mechanism comprising a motor having an output shaft, a crank mounted on said output shaft and connected to said operating rod at said center cf percussion, said crank including a counterweight positioned diametrically opposite to the connection of said operating rod for counterbalancing the load connected thereby.

9. A nutation apparatus comprising a member to be nutated, a yoke member pivotally connected thereto for relative rotation about a first axis, said nutated member including pivotal supporting devices for support thereof for rotation about a second axis substantially perpendicular to said first axis, said yoke member inclucling at least two balancing weights for equalizing the moments of inertia and for making the centers of percussion of the combination of said members coinciclent for rnovernent about either axis, said yoke member also including an operating rod extending therefrom away from both 0f said axes at least as far as to said coincidlent centers of percussion, a drive mechanism cornprising a motor having an output shaft, a crank mounted on said output shaft and connected to said operating rod at said center ot percussion, said crank including a counterweight positioned diametrically opposite to the connection of said operating rod for counterbalancing the load connected thereby.

10. A non-rectilinear nutation system for a directional high frequency radiation antenna comprising an antenna dish of conductive material, a yoke member, said dish being pivotally mounted on said yoke member for limited rotation about a first axis, fixed pivotal supports for said yoke member for limited rotation thereof about a second axis substantially perpendicular to said first axis, said dish including counterweights horizontally spaced from the central portion thereof for equalizing the moment of inertia of said dish about said first axis with the combined moment of inertia of said dish and said yoke member about said second axis, an operating rod fixed to said dish and extending therefrom, said operating rod being positioned to include a point representing a cornrnon center of percussion for said dish for rotation about said first axis and for the combination cf said dish and said yoke for rotation about said second axis, a drive mechanism connected to drive said operating rod at said center of percussion, said drive mechanism including a counterbalanced crank at said connection to said operating rod, and a motor having an output shaft eonnected to rotate said crank.

11. A rectilinear nutation system for a dilrectional high frequency antenna comprising a dish-shaped antennamember, relatively fixed pivotal support members fastened to said antenna for support thereof for rotation about a first axis, a yoke member pivotally mounted to said dish member for rotation with respect thereto about a second axis perpendicular to said first axis, said yoke member including an operating rod extending outwardly therefrom, said yoke member also inclutling counterweights mounted thereto by means of counterweight arms extending away from said yoke member in directions substantially perpendicular to said second axis to increase the moment of inertia of said yoke about said second axis to correspond to the moment of inertia of the combination of said yoke and said dish member about said first axis, said operating rod being positioned to intersect a point corresponding to the center of percussion of said yoke about said second axis and of said yoke and dish about said first axis, and a drive mechanism cornprising a coun terweighted crank connected to said operating rod at said center of percussion point, and a motor eonnected for rotating said crank.

N0 refereuces cited. 

